User blog:Samuli.seppanen/Some thoughts on reconstructing ballistas
After a hectic January at work it seems things have finally calmed down a bit, and I can resume my project. First a few thoughts about recontructing ballistas, or any ancient weapons for that matter. When I've talked about the cheiroballistra reconstruction project with other people of various backgrounds, it seems that putting oneself into the shoes of the Romans who actually used the cheiroballistras is quite difficult. After pondering about this a bit, I think one needs to approach this problem by asking these two questions: # What was the purpose of the cheiroballistra? # What properties did it need to fulfill this purpose? The answer is clear in my opinion: the cheiroballistra was a weapon designed to kill (possibly) armored people at long ranges. If a modern reconstruction falls short on that goal it is not worth much, and the amount of conclusions one can draw from the results are severely limited. Of course in modern times we're not going to kill people with our reconstructions, but the reconstruction still needs to have that capability to be considered successful. Academic cheiroballistra reconstructions in the past have suffered from one or more of the following issues: # They exist only on paper # They have really bad performance # Their performance figures (velocity, kinetic energy) have not been published, almost certainly due to #2 # The measurements in the manuscript have been changed arbitrarily in the name of correcting errors/omissions in the text The cheiroballistra needed an edge over similar weapons such as bows, gastraphetes, arcuballista, slings and whatnot. In my tests a stomach-cocking cheiroballistra can shoot about 2-3 bolts a minute with a little practice. With a bow a professional can provably shoot a few arrows a second in short bursts. Even with Victorian style shooting with a quiver one can easily shoot 10 arrows a minute. Although the range of the ancient bow is not exactly know, I believe the effective range is given as ~150 meters in Vegetius text. The extreme range would probably be around 250 meters. Fortunately we have plenty of modern evidence about the performance of bows of various constructions, so we're not entirely at the mercy of ancient manuscripts. So, having a cheiroballistra that shoots to 200 meters or so (e.g. Wilkins) and weighs nearly 30 kilos would be utterly useless in the battlefield or in a siege. The reconstruction by Stevenson (~300 meters) is better, but still not nearly enough. Nick's FireFly's 900 meters is enough to give an edge over the non-torsion projectile weapons of the era. I have not tested my reconstruction's maximum range because it has not been pumped to full power yet. That said, even in its last working state it could launch reasonably sized bolts at same velocities as the FireFly, so a very conservative estimate for the maximum range is 500 meters, but I suspect 700 meters is doable. It probably can't reach FireFly's range because it shoots bolts which are significantly lighter and thus lose energy and velocity faster. Another choice one has to make when reconstructing the cheiroballistra is how strictly to follow the dimensions given in, or derivable from, the manuscript. Without practical experience in high-power reconstructions there is an easy answer: "just stick with the numbers in the text". However, the manuscript and practical tests don't always meet. For example, Iriate (2000: 56) calculated that the thickness of the field frame bars should be 5-6mm. This may be barely enough for a full-power reconstruction, especially if the parts are made from high-quality steel. My current bars are 8mm thick, and under high (350hz) pretension they bend visibly, even though not excessively. It may be worth a try to go back to 6mm bars when I create another set of field frames and washers for use with sinew springs, but for now 8mm seems a more correct choice. This brings us to another point: there are measurements which are very important to adhere to, such as the spring diameter. If one increases the spring diamater then all hell breaks loose because this single change forces one to change measurements elsewhere. This, in turn, causes other components to drop out of balance and to become too weak. Wilkins (1995) reconstruction is a prime example of this - he was forced to make the cones from bronze because wooden cones of the dimensions given in the text broke early in the draw. The bronze cone theory is just a crude attempt to patch over a misinterpretation without violating the manuscript's instruction. The thing is that it would have been much easier to just forge the arms from one piece of steel instead of using a complex bronze/steel composite construction. From my experience (~10 iterations of arms) I can tell that making arms that can take a full-power draw is very tricky even with the spring diameter given in the manuscript. Using wooden cones of manuscript's dimensions with an enlarged spring diameter would be impossible. The Greek text contains hints into how the manuscript was used and by whom. Typically the English translations lose quite a few nyances, because English lacks singular and plural third-person imperative forms (see Translation of Cheiroballistra). Those forms make it pretty clear that the manuscript was aimed at an engineer who had craftsmen (woodworkers, blacksmiths, etc.) at his disposal. For example, the text starts with "They shall produce two dovetailed beams, ΑΒ and ΓΔ...". In practice the Roman blacksmiths must have aimed at the dimensions given in the text, but they would have been told by an engineer where preciseness was particularly important. This is clearly proven by the pi-brackets in the existing archaeological field frames: they vary widely in shape and size, and that is, in my opinion, partly because of structural differences (e.g. wooden vs. iron beams in the little ladder) and partly because of "it does not matter in practice". In the course of my work I've shown that it is possible to follow instructions in the text and, with minimal amount of assumptions, to create a viable, high-power weapon. That was my original assumption, and there is still no reason to think otherwise. Category:Blog posts Category:Backup